Carrier telegraph receiver



June 9, 1936. L. E. MELHUISH 2,043,355

' I CARRIER TELEGRAPH RECEIVER Filed Dec. 29, 1954 AAAAA POLARIZILD/ 3WM INVENTOR L .E. MELHU/SH ATTORNEY Patented June 9, 1936 PATENT OFFICECARRIER TELEGRAPH RECEIVER Lawrence E. Melhuish, Glen Ridge, N. J.,assignor to Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application December 29,1934, Serial No. 759,667

1 Claim.

The present invention relates to signaling and more particularly to thereception of signal waves or impulses by rectification.

The invention will be described with particular reference to carriertelegraphy although it is capable of more general use. In signalingsystems, such as in carrier telegraphy, variations in line equivalenttend to give rise to faulty reception on account of the variation instrength of received signals. It is diificult to set a receiving printeror other recorder to be equally responsive to received impulses ofwidely differing strength. Consequently, it is customary for anattendant from time to time to change the adjustments of a receiver tosuit the different line current conditions.

It is an object of the present invention to provide a signal receivingcircuit which will respond equally to received current impulses thatvary in strength from time to time.

This object is attained in accordance with the invention by providing inthe circuits that operate the receiving relay, two circuit branches thatare mutually opposed in their effects on the relay, and so adjustingthese efiects that the resultant is substantially constant throughout arange of received signal strengths.

In the drawing, to which reference will now be made for a more completeunderstanding of the nature and objects of theinvention,

Fig. 1 is a schematic circuit diagram illustrative of a system to whichthe invention is applicable; and

Fig. 2 shows a modified type of receiving circuit in accordance with theinvention.

In Fig. 1 the line I is shown terminating at the left in a transmittingstation and at the right in a receiving station. The transmittingstation is indicated as comprising a number of transmitters of which twoare shown at 2 and 3 each provided with a source of carrier waves as at4 and 5, respectively. Other similar transmitters may be provided. Itwill be understood that each of these transmitters will include anysuitable means for controlling the carrier wave in accordance withsignals to be transmitted such as an interrupter or other suitable typeof sender together with any filtering elements that may be required, allin accordance with well-known practice in this art.

At the receiver filters are provided as at B and 1, for separatingreceived currents into various channels, there being as many of thesefilters as there are channels to be received at this station. Thesefilters may be the usual type of band filters or tuned circuits or othersuitable selective networks. Only the channel associated with the filter6 is shown in detail, it being understood that the other receivingchannels will be similarly equipped.

The output of the filter 6 is connected through transformer Ill to theinput circuit of a tube I2 which serves as an amplifier for the receivedsignals. The tube I2 is shown as of the screen grid type. A screen gridor pentode or similar type of tube having a high amplification ispreferably employed. The output of the amplifier tube I2 is connected toa rectifier 'or detector tube. I3 containing a polarized relay I4 in itsoutput. Space current for the tube I2 is supplied from battery I!through resistance I8. This combination of battery II and resistance I8is in parallel with battery 20 and resistance I9 for a purpose to bedescribed presently. Condenser 23 is a by-pass condenser for thealternating component of the received amplified waves.

When there is no incoming signal from the filter 6 the grid of the tubeI2 is made so far negative by the grid battery 24 that no space currentflows through this tube. Under these conditions the voltage of thebattery 20 is adjusted to such a value with respect to the resistancesI8 and Is that current is forced to flow from the battery I? throughresistances I8 and I9 in series and into the battery 2|] against thevoltage of that battery. There is thus a voltage drop produced in the resistance I9 in such a direction as to make the grid of the detector tubeI3 negative with respect to the filament. The slider 22 on resistance I9and the other elements of the circuit, if necessary, are proportioned oradjusted so that under these conditions the space current of the tube I3is zero and the winding I5 of the relay I 4 is therefore withoutcurrent. The bias winding, supplied with suitable current from a batterythrough a regulating resistance, as shown, is used to keep the armatureagainst the spacing contact under these conditions.

An incoming signal through the filter 6 is applied through the highstep-up ratio transformer II) to the grid of tube I2 driving the grid ina positive direction and reducing the internal impedance of the tube I2to a low value. Plate current is thus drawn from the battery I'I throughthe resistance I8 causing a substantial voltage drop in resistance I8sufiicient to permit the battery 20 also to supply space current to thetube I2 through its resistance I9. The consequent reversal of currentthrough the resistance I9 changes the potential of the grid of tube I3from its normal highly negative value to a positive value Operating therelay M to its marking contact.

The elements of the circuit are proportioned preferably so that thedetector tube 3 will be subject to grid voltage swings beyond normalcapacity, for example, grid swings of the order of volts. This willresult in a space current through the tube l3 of zero value on spacingand of a value limited chiefly by the value of the resistance for themarking condition. The bias current in the winding l6 of the relay isset at the optimum value for this current. The constants of the vacuumtube circuit including the interstage elements are preferablyproportioned so that the space current of the tube i3 is changed fromits zero value to its maximum value by any input voltage in excess of adefinite minimum operating voltage. This results in the relay Mreceiving substantially the same operating current for both weak andstrong received line current signals.

In the alternative receiving circuit shown in Fig. 2, the output of thefilter 6 leads through transformer 33 to a rectifier 3| which is shownas of th solid element type in bridge circuit conion. The rectifiers arepreferably of the copper-oxide type although any suitable type ofrectifier may be used. The direct current terminals of the rectifier 3!are connected across a high resistance 32 and also to the terminals ofwinding of receiving relay 3d. The resistance S2 is so high that for anygiven rectified signal substantially all of the current flows throughthe winding 36 and very little flows through the resistance 32.

A vacuum tube amplifier 33 has its grid circuit connected across avariable portion of high resistance 32 and has its plate circuitconnected to the winding 35 on relay 34. Relay 34 is a polarized relayhaving a biasing winding 31.

In the operation of the circuit of Fig. 2 when there is no incomingsignal the grid bias of the amplifier tube 33 is so far negative that nocurrent flows through the winding 35. Since there is also no rectifiedoutput from rectifier 3! there is no current in the winding 36. Underthese conditions the current in the bias winding 31 holds the armatureagainst the spacing contact.

Upon the receipt of signal waves through the filter 6, these waves arerectified at 3| and the rectified current flows through the winding 36causing the relay 34 to operate to shift its armature from the spacingto the marking contact. Some of the rectified output flows throughresistance 32 and produces a voltage on the grid of the tube 33 in adirection to permit current to flow through the tube 33 and through thewinding 35. The effect of this current in the winding 35 opposes theeffect of the rectified current in the winding 36 so that the resultanteffect of both of these windings on the relay 34 is a differentialeffect, the effect of winding 36 always predominating.

As the line equivalent of the line I changes and the strength of thereceived signals varies from time to time, it will be apparent that theadjustments of the circuit may be so made that stronger current in thewinding 36 resulting from stronger signals are opposed by strongercurrent in the winding 35, tending to give a net resultant effect on therelay 34 which may be made substantially constant over a wide range ofvariation of strength of the received signals.

The relay 34 is in this way made to respond substantially equally toboth weak and strong received signals.

it is contemplated that amplifiers will be introduced into the circuitsof Figs. 1 or 2 as may be required either at the transmitter or at thereceiver or both. In Fig. 2 particularly, it will be necessary inpractice to use amplification in order to provide a requisite amount ofenergy for properly operating the rectifier 3i and for making up thelosses in the rectifier.

It will be understood that the invention is not to be construed aslimited to the specific details have been shown and described, but thatthe invention is susceptible to variation or modification within thescope and spirit of the appended claim.

What is claimed is:

In a receiving circuit for a. system having a transmission equivalentsubject to change, a rectifier for the received signal waves, a relay,the output current from said rectifier including a winding on said relayfor actuating the relay, a vacuum tube having in its output circuit awinding on said relay for opposing the effect of said first winding, theinput of said vacuum tube being connected to the output circuit of saidrectifier, the circuit elements being proportioned such that the effecton the relay operation of the second mentioned winding is always weakerthan that of the first winding whereby a differential effect on therelay is produced which is substantially constant over a range ofvariation of received signal strengths.

LAWRENCE E. MELHUISH.

